Prokaryotic Genetic Regulation

Question 1

Conditions for an “Active” Gene

Answer 1

• The DNA can be transcribed
• The mRNA can be translated
• The enzyme produced can be activated

Question 2

Control Mechanisms

Answer 2

• Positive (Apoinducer attached when transcription is ON)
• Negative (Repressor is off DNA when transcription is ON)
• Inducible (High conc. of inducer when transcription is ON)
• Repressible (Low conc. of corepressor when transcription is ON)

Question 3

Lac Operon is…

Answer 3

Negative inducible

Question 4

Trp Operon is…

Answer 4

Negative repressible

Question 5

Catabolite Repression is…

Answer 5

Positive inducible (cAMP = inducer)

Question 6

Attenuation Mechanism

Answer 6

1. Leader region (before the genes) contains 4 regions
2. R1 makes a nonfunctional protein (and has S-D before it)
3. R1 translates as R2 is transcribed
4. Translation is dependent on relevant amino acid concentration (e.g. Trp)
5. If AA is high, then translation is fast, and the ribosome reaches R2 before R3 is transcribed, which causes R3 and R4 to form a termination hairpin and stop transcription
6. If AA is low, then translation is slow, and the ribosome does not reach R2 before it pairs with R3 to form an anti-termination hairpin, which frees R4 and allows transcription to move onto the first gene; ribosome disrupts R2-R3 pairing and allows R3 and R4 to form termination hairpin after polymerase has moved beyond it